1. Field of the Invention
The present invention relates to a combination type thin film magnetic head having a writing inductive type thin film magnetic head and a reading thin film magnetic head including a magnetoresistive element, said heads being stacked on a substrate, and a manufacturing method thereof.
2. Explanation of the Related Art
Recently, a surface recording density of a hard disk drive has been improved, and the performance of a combination type thin film magnetic head has to be improved accordingly.
As a combination type thin film magnetic head, a head having an inductive type thin film magnetic head for writing and a magnetoresistive type thin film magnetic head for reading, which are stacked one on the other on a substrate, has been proposed and has been put to practical use. In general, an element using a conventional anisotropic magnetoresistive (AMR) effect has been used as a reading magnetoresistive element. Still, an element using a giant magnetoresistive (GMR) effect, which has a larger resistance variation ratio than the AMR element by several times, has been developed.
In this specification, the AMR element and the GMR element or the like are referred to as a magnetoresistive type thin film magnetic head generically, or simply an MR element.
The surface recording density of several giga (G) bits per inch 2 can be realized by using the AMR element. Moreover, the surface recording density can be more improved by using the GMR element. In this way, the realization of a hard disk drive device in 10 G byte or more becomes possible by raising the surface recording density.
One of factors for determining the performance of the reproducing head including such a magnetoresistive reproduction element is a height of the magnetoresistive reproduction element (MR height MRH). The MR height MRH is a distance of the magnetoresistive reproduction element whose edge is exposed to an air bearing surface measured from the air bearing surface. In the manufacturing process of the thin film magnetic head, desired MR height MRH is obtained by controlling an amount of polishing when the air bearing surface is polished.
On the other hand, in accordance with the improvement in the performance of the reproducing head, the performance of the recording head is required to be improved. It is necessary to raise the density of the truck on a magnetic recording medium in order to improve the surface recording density. For this purpose, it is necessary to make the width of a write gap on the air bearing surface narrow from several microns to the sub-micron order. The semiconductor processing technology is used to achieve this.
A throat height (TH) is one of the factors for deciding the performance of the writing thin film magnetic head. The throat height is a distance of a magnetic pole portion measured from the air bearing surface to an edge of an insulating layer by which a thin film coil is separated electrically, and it is desired to shorten this distance as much as possible. Reduction in size of the throat height TH is also decided by the polishing amount on the air bearing side.
Therefore, in order to improve the performance of the combination type thin film magnetic head, that is, one that includes stacked reading magnetoresistive type and writing inductive type thin film magnetic heads, it is important to make the writing inductive type thin film magnetic head and the reading magnetoresistive type thin film magnetic head well balanced.
FIGS. 1-9 show successive steps of manufacturing a conventional standard thin film magnetic head, in each figure, A is a cross sectional view of the entire thin film magnetic head, and B is a cross sectional view of the magnetic pole portion. Moreover, FIGS. 10-12 are a cross sectional of the entire conventional completed thin film magnetic head, a cross sectional view of the magnetic pole portion, and a plan view of the entire thin film magnetic head, respectively. In this embodiment, the thin film magnetic head is a combination type formed by stacking the readout inductive type thin film magnetic head and the reading MR reproduction element.
At first, as shown in the FIG. 1, an insulating layer 2 consisting of, for example, alumina (Al.sub.2 O.sub.3) is deposited on a substrate 1 made of AlTiC in the thickness of about 5-10 .mu.m. Next, as shown in the FIG. 2, a first magnetic layer 3 constituting one magnetic shield protecting a MR reproduction element of a reproducing head from the influence of the external magnetic field is formed with the thickness of 3 .mu.m.
Then, as shown in the FIG. 3, after alumina is deposited by sputtering with the thickness of 100-150 nm, as an insulating layer 4, a magnetoresistive layer 5 made of a material having the magnetoresistive effect and constituting the MR reproduction element, is formed with the thickness of 10 nm or less, and then, is formed into a desired shape with a mask alignment of high accuracy.
Then, as shown in FIG. 4, another insulating layer 6 is formed such that the magnetoresistive layer 5 is embedded between the insulating layers 4 and 6.
Next, as shown in FIG. 5, a second magnetic layer 7 made of a permalloy is formed with a film thickness of 3 .mu.m. The second magnetic layer 7 not only functions as the other shield for magnetically shielding the MR reproduction element together with the first magnetic layer 3, but also functions as one pole of the writing thin film magnetic head.
Next, after a write gap layer 8 made of a non-magnetic material, for example, alumina, is formed with a thickness of about 200 nm on the second magnetic layer 7, a magnetic layer made of a magnetic material having a high saturation magnetic flux density, for example, permalloy (Ni: 50 wt %, Fe: 50 wt %) and nitride iron (FeN), is formed. This magnetic layer is shaped into a desired form with a mask alignment of high accuracy to obtain a pole chip 9. The track width is defined by a width W of the pole chip 9. Therefore, it is necessary to narrow the width W of the pole chip 9 in order to achieve a high surface recording density.
In this case, a dummy pattern 9' for connecting the second magnetic layer 7 with a third magnetic layer constituting the other pole, is formed at the same time. Then, after mechanical polishing or chemical mechanical polishing (CMP), a through-hole can be formed easily.
In order to prevent the effective write track width from being widened, that is, in order to prevent the magnetic flux from being widened at one pole during the data writing, the gap layer 8 in surroundings of pole chip 9 and the second magnetic layer 7 constituting the other pole are etched by the ion beam etching such as the ion milling. This state is shown in FIG. 5. This structure is called as a trim structure, and this portion becomes a magnetic pole portion of the second magnetic layer.
Next, as shown in FIG. 6, after forming an insulating layer 10 such as an alumina film having a thickness of about 3 .mu.m, the surface is flattened by for example CMP.
Afterwards, after an electrically insulating photoresist layer 11 is formed to a predetermined pattern by the mask alignment with high accuracy, a first layer thin film coil 12 of, for example, copper is formed on the photoresist layer 11.
Then, as shown in FIG. 7, after forming an insulating photoresist layer by the mask alignment with high accuracy on the thin film coil 12, the surface is flattened by baking at the temperature of, for example, 250-300.degree. C.
In addition, as shown in FIG. 8, a second layer thin film coil 14 is formed on the flattened surface of the photoresist layer 13. Next, after forming a photoresist layer on the thin film coil 12 by the mask alignment with high accuracy, the surface is flattened by baking at the temperature of, for example, 250.degree. C.
As described above, the reason for forming the photoresist layers 11, 13, and 15 by the mask alignment with high accuracy is to define the throat height TH and the MR height MRH by using the edge of the photoresist layer on the side of magnetic pole portion as a standard position.
Next, as shown in FIG. 9, a third magnetic layer 16 constituting the other pole is selectively formed with the thickness of 3 .mu.m on the pole chip 9 and photoresist layers 11, 13, and 15 by for example a permalloy according to the desired pattern.
The third magnetic layer 16 is contacted with the second magnetic layer 7 at a rear position away from the magnetic pole portion by means of the dummy pattern 9', so that the thin film coils 12 and 14 pass through a closed magnetic path constituted by the second magnetic layer 7, the pole chip 9, and the third magnetic layer 16.
In addition, an overcoat layer 17 consisting of alumina is deposited on the exposed surface of the third magnetic layer 16.
Finally, the side surface on which the magnetoresistive layer 5 and the write gap layer 8 are formed is polished to form an air bearing surface (ABS) 18 that is opposed to a magnetic recording medium during use.
The magnetoresistive layer 5 is also ground during the formation of the air bearing side surface 18, and thus an MR reproduction element 19 is obtained. In this way, the above mentioned throat height TH and MR height MRH are decided. The state thereof is shown in FIG. 10. In actual thin film magnetic head, pads for making electric connections to the thin film coils 12, 14, and MR reproduction element 19 are formed, but they are not shown. Moreover, FIG. 11 is a cross sectional view in which the magnetic pole portion of the combination type thin film magnetic head formed thus was cut by a plane parallel to the air bearing surface 18.
As shown in FIG. 10, an apex angle .theta. between a segment S for connecting corner portions of side surfaces of the photoresist layers 11, 13, and 15 isolating the thin film coils 12 and 14 and the upper surface of the third magnetic layer 16, is also an important factor for determining the performance of the thin film magnetic head together with the above mentioned throat height TH and MR height.
Moreover, as shown in the plan view of FIG. 12, the width W of the pole chip 9 and the magnetic pole portion 20 of the third magnetic layer 16 is narrow. Since the width of the track recorded on the magnetic recording medium is determined by this width, it is necessary to narrow the width W as small as possible to achieve a high surface recording density. Moreover, in FIG. 12, for the sake of simplicity, the thin film coils 12 and 14 are shown by concentric circles.
Well, up to now, in the formation of the conventional thin film magnetic head, a particularly difficult problem after the formation of the thin film coils, is a miniaturization of the top pole formed along the coil projection, especially along its inclined portion (Apex) covered by the photoresist insulating layer.
That is, the given pattern is formed by depositing the photoresist with the thickness of 3-4 .mu.m after a magnetic material such as permalloy is plated to form the third magnetic layer on the coil projection having the height of about 7-10 .mu.m, and then the desired pattern is obtained by using the photolithography technology.
Here, if the thickness of 3 .mu.m or more is necessary for as the resist film patterned by the photoresist on the recessed portion of the mountain like coil, the photoresist of the thickness of about 8-10 .rho.m will be deposited at a root portion of the inclined portion.
On the other hand, in the third magnetic layer formed on the surface of the coil mountain portion, which has such a height of about 10 .mu.m, and on the flat write gap layer, a narrow track of the recording head is formed near the edge region in the photoresist insulating layer (for example, 11 and 13 in FIG. 7), so that the third magnetic layer must make the pattern with a width of about 1 .mu.m. Therefore, the necessity for forming the pattern with width of 1 .mu.m is achieved by using the photoresist film of a thickness of 8-10 .mu.m.
However, even if you form the narrow pattern with about 1 .mu.m width with a thick photoresist film such as 8-10 .mu.m, the crumble of the pattern etc. according to reflected light are generated during exposure due to photolithography and the decrease in the resolution happens due to the thick resist film, so that it is extremely difficult to pattern the narrow top pole used to form a narrow track, accurately.
Then, as shown in the above conventional embodiment, assuming that data is written by the pole chip that forms the width of the narrow track recording head, it is proposed to reduce the above problem by applying a method in which the third magnetic layer is connected to the pole chip after the pole chip is formed. In other words, the structure is divided in two, the pole chip determining the width of the track and the third magnetic layer introducing the magnetic flux.
However, the following problems remain unsolved in the thin film magnetic head formed as described, especially in the recording head.
(1) The positional relationship of the pole chip 9 and magnetic layer 16 is decided by the alignment of photolithography, so that when viewing from the air bearing surface, there is a possibility that the central line of the pole chip and the central line of the third magnetic layer are shifted greatly, the leakage of magnetic flux might occur, and data might be written by the leakage flux from the third magnetic layer, an effective track width might be increased, and there is a problem of writing data on an adjacent track. It is necessary to widen the truck interval to avoid this problem, and thus the surface recording density will not be improved.
(2) The narrow pole chip 9 is brought into contact with the wide third magnetic layer 16 vertically. The magnetic flux is liable to be saturated at this contact portion. Therefore, a satisfactory improvement of writing characteristic (Flux Rise Time) is not obtained.
(3) The throat height TH and MR height MRH are decided based on the edge of the insulating layer isolating the thin film coil on the air bearing side, but this insulating layer is deformed easily by heat, because the insulating layer is usually formed by an organic photoresist insulating layer. Therefore, this insulating layer is deformed by heating treatment at about 250.degree. C. during the formation of the thin film coil, and the pattern size of the insulating layer changes, so that the size of throat height TH and MR height might deviate from desired design values.
(4) It is necessary to shorten the throat height TH as much as possible to improve the magnetic property of the inductive type thin film magnetic head and to achieve the small size, but in the conventional combination type thin film magnetic head, a reference position of throat height zero is determined by the position of the edge of the magnetoresistive layer opposite to the air bearing surface, and can not be located at the side of the air bearing surface, therefore, there is a problem that the throat height TH cannot be shortened.
(5) In the reading thin film magnetic head consisting of the magnetoresistive element, it is advantageous to use the GMR element with high sensitivity as a magnetoresistive element, but there is a problem that the reading sensitivity of the GMR element is deteriorated by the heating treatment at about 250.degree. C. performed for the photoresist film when the thin film coil of the inductive type thin film magnetic head is formed.
(6) The GMR element of high sensitivity has a structure formed by stacking different kinds of thin films of 1-5 nm. Therefore, many manufacturing steps are required for forming the GMR element to complete the combination type thin film magnetic head. Since electrostatic breakdown occurs during handling, the many required steps may cause a decrease in the manufacturing yield.
(7) The alumina film having a thickness of 30-40 .mu.m or more is formed as the overcoat layer at the end of the mass production process of the combination thin film magnetic head to protect the device and to stabilize the quality. A warp might be generated in the substrate, and many particles are generated by the sputtering used to form the alumina film, so that the device characteristic may deteriorate and defective components may be produced. Moreover, as described above, a long time of 15 hours or more is necessary to form a thick alumina film by sputtering. Therefore, the throughput might be extremely decreased. Additionally, a long time is required for the etching to expose the contact pads of the electrode pattern for the magnetoresistive element.
(8) In the combination type thin film magnetic head, the characteristics of the combination type thin film magnetic head are mainly determined by a width and MR height MRH of the magnetoresistive element of the magnetoresistive type thin film magnetic head, a width of the magnetic pole portion, a throat height TH, and characteristic of NLTS (Non-Linear Transition Shift ) for the inductive type thin film magnetic head. Therefore, the requirement of user has concentrated on these specifications. For example, since the width of the magnetoresistive element is decided at an early step of the manufacturing process, when a particular width is specified by a user, a time period until the product is completed, that is, the cycle time becomes very long, and sometimes amounts to 30 to 40 days.